Sunday, March 30, 2014

Got this pulse monitor from eBay, advertised as broken. When paired with a phone it always showed 100 bpm. Searching a bit on the Internet saw that quite a few people had this problem as well ("stuck at 100 bpm").

The front has three buttons, the middle one being pairing/on/off and the left and right ones supposedly change the tracks on your phone media player. Controls seem very similar to the bulk of bluetooth headphones.
The backside has the sensor in the upper part - I suspect the pulse-oximeter type one - and two round pads for the charger dock.

It's clear now why the bracelet does not give any readings:

Due to bad engineering there is no proper strain relief for the wires between the sensor and the controller.
I'm inserting a link break here since this post a lot of pictures.

This came out of a "box of things" that I regularly purchase on eBay. They consist of new items that are DOA (dead on arrival).

It's a "Spy Pen" or "Spy Stick" - a USB stick with a 4GB capacity that also has a camera inside.

The second line under the title makes absolutely no sense, it's like someone used OCR + Google Translate:

The end cap was unglued, also the stick would not take a charge. With a bit of force the motherboard slides out, revealing a camera module that's literally plugged in:

Great, I get a 4GB microSD for free:

Also notice the reset button, I have no idea what's that for, I assume pressing it while plugging the stick in will allow uploading new firmware. Also, the battery is held in position with sticky tape.
The other big chip is a 25Q80SCP, 8Mbit flash, probably holding the camcorder firmware.

A clearer picture of the battery side with the camera connector. I don't know what this chip is but I assume it's an integrated solution for cheap camcorders: Anyka AK1120Q06402:

The battery was dead so I tried removing the kapton tape and access the third terminal. This allowed me to bypass the protection circuit and charge the small battery.
When charging an unknown LiPo the safest maximum setting is 1C - in this case 160mAh. Just be aware of the fact that many manufacturers fake the printout, putting you at risk of overdriving the small LiPo and causing it to explode. Your best bet is to find a similar-sized battery that is original and use that capacity as guideline

With the battery off the camera can still be used, it draws around 50mA which would make it perfect for a flight cam or other small embedded project:

The "innovative" packing method is used to put the pen back together:

Hopefully I will remember to put some samples from the camera here, the quality is not so bad as I would have expected. It's certainly better than most camera phones pre-smartphone-era.

This post is just to make people aware of a project that I did a while back.

I was annoyed that the Spektrum DX6i remote that I had did not provide the useful timer features of the DX8i. That is, the countdown timer should be automatically activated when the throttle is actuated instead of requiring the user to manually pull on the trainer switch.

Hardware and firmware side together this hack took me around one hour to complete so it should take you much less should you consider to perform it.

I've spent another hour retrofitting the display backlight and adding that functionality to the firmware as well.

Features:

- one PIC10F222 (<1$ in single units)

- can detect whether single-pitch (plane mode) or collective pitch is used

- starts timer on throttle up, stops it when throttle is removed

- backlight is activated when the menu wheel is moved, deactivated after 5s

- inactivity warning: after 90s of no usage the remote beeps at you

- features can be disabled at startup by powering up the remote with the throttle in the high position